The present invention relates to an eddy current sensitivity setting standard and a method for using the eddy current sensitivity setting standard.
In the past, an eddy current sensitivity standard was fabricated by machining an EDM slot into the critical inspection area of a section of a part to be inspected. The use of a section of the inspected component as the standard was critical because the typical eddy current probe responds to numerous benign electrical changes (electrical conductivity and permeability) induced by interaction with the metal surface under inspection other than those produced by a flaw such as a crack. Typically, the eddy current probe is sensitive to surface roughness, variations in conductivity/permeability within acceptable limits, geometric variations along the scan path, such as edges, radii, and/or slots, liftoff, and the like. All inspection surface parameters that affect the eddy current signal must be simulated in the standard to produce an accurate eddy current signature. If all the parameters affecting the eddy current response were not represented in the standard design, it would be impossible to separate the effects of the benign surface electric and geometric variations from a defect response.
As components being inspected are now extremely expensive, it has become impractical to consume good hardware to produce the multiple inspection standards needed to establish common reject levels for each component inspected. Machining facsimile/duplicates of the inspected component from the same material is very expensive and does not truly represent the conditions encountered on the inspection surfaces of the service run hardware. Slight alterations to field engine components induced by engine operating extremes such as high temperature, wear, oxidation/sulfidation or, as is the case with most compressor disk blade slots, galling along the disk/blade contact surface, are often acceptable for continued operation, but greatly affect the eddy current scan baseline to the point of potential rejection of flight worthy hardware. These types of surface artifacts are not reproducible in a manufactured facsimile standard.
Accordingly, it is an object of the present invention to provide an eddy current sensitivity setting standard which can be easily applied and which is accurate.
The foregoing object is attained by the compliant laminar eddy current sensitivity standard.
In accordance with the present invention, a compliant laminar eddy current sensitivity standard is provided. The compliant laminar eddy current sensitivity standard comprises a sheet of nonconductive, nonmagnetic material, at least one strand of highly conductive material embedded in the nonconductive, nonmagnetic material, and an adhesive layer attached to a surface of the nonconductive, nonmagnetic material.
A method for using a compliant laminar eddy current sensitivity standard comprising the steps of providing a sheet of nonconductive, nonmagnetic material with at least one strand of highly conductive material embedded in the nonconductive, nonmagnetic material, and an adhesive layer attached to one surface of the nonconductive, nonmagnetic material; adhering said sensitivity standard on said surface of said part; and moving an eddy current probe over a surface of said sensitivity standard.
Other details of the compliant laminar eddy current sensitivity standard of the present invention, as well as other objects and advantages attendant thereto, will be set forth in the following detailed description and the accompanying drawings, wherein like reference numerals depict like elements.